Investigation of the Soret coefficient in magnetic fluids using the Z-scan technique

The generalized thermal lens model formalism, which includes on it the thermodiffusion phenomenon, is used to determine the Soret coefficient (ST) of a cationic surfacted ferrofluid. The single-beam Z-scan experiment is employed to obtain both the magnitude and sign of ST. Besides ST, the method allows the determination of the parameter ∂n/∂I, where n and I are the sample index of refraction and the incident laser beam intensity on the sample. This parameter accounts for the third-order nonlinear optical effects which yield in the sample an instantaneous modification of the index of refraction, proportional to the intensity of the local light.